TURNING STARS INTO GOLD
Many common elements, such as oxygen and carbon, are known to be made
in stars and distributed through the Universe when a star explodes as
a supernova. This is the origin of most of the material that makes up
the Earth. It is becoming clear, however, that normal stars cannot
make enough of the heavy elements, such as gold and platinum. Thus the
origin of gold and platinum - on Earth and throughout the Universe -
remains a mystery.
Dr Stephan Rosswog and co-workers from the Universities of Leicester
and Basel, Switzerland, will be reporting to the UK National Astronomy
Meeting on Thursday 5 April about a new way to make gold, platinum and
other heavy elements.
COLLIDING NEUTRON STARS AND PRECIOUS METALS
Rosswog's team has explored the idea that these heavy elements were
formed in the violent collisions of super-dense neutron stars. These
stars - the dead cores of old stars - weigh a million times more than
the Earth but are only the size of London.
Neutron stars are sometimes found close together in pairs and
Dr. Rosswog has calculated what happens when these binary stars are
close enough to collide. In addition to a huge amount of energy
released - enough to fuel the most powerful explosions in the Universe
(known by astronomers as gamma-ray bursts) - he has found that a large
quantity of gold and platinum is made and thrown out into space.
Dr Rosswog's calculations were made on a new supercomputer at the UK
Astrophysical Fluids Facility (UKAFF) based in Leicester. The UKAFF
computer is one of the first Origin 3800 supercomputers made by
Silicon Graphics Inc. It is special because it has 128 processors that
can work together in parallel on a single problem. Together with 64GB
of RAM and 1300GB of disk space, this is the most powerful computer in
Europe dedicated to astronomical calculations. It began operation in
October 2000, making Dr Rosswog's calculations possible for the first
time.
The calculations are difficult because they include a lot of exotic
physics, including the effects of quantum mechanics and Einstein's
general theory of relativity. Dr. Rosswog builds two model neutron
stars in the UKAFF computer, and starts his calculation with them
close enough for Einstein's theory to force them to spiral
together.
A single calculation takes weeks on the supercomputer, representing
just the final few milliseconds in the life of the two stars. As they
spiral closer, immense forces tear them apart, releasing huge amounts
of energy - enough to outshine the entire Universe for a few
milliseconds. The stars collapse to form a black hole, but
Dr. Rosswog's calculations show that some of their material is thrown
out into space (images of the simulation are available on the UKAFF
website - see below).
This explosive ash is still extremely dense and hot, around a billion
degrees Celsius, allowing the necessary nuclear reactions to take
place. Relatively small seed nuclei, made of elements like iron,
collect neutrons and build themselves up to become heavy elements such
as gold and platinum. The ash, now containing gold and platinum,
gradually cools down and continues to fly out into deep space. It
mixes with the gas and dust between stars that eventually, in turn,
collapse down to form new generations of stars.
Dr. Rosswog and his colleagues have shown that the relative amounts of
elements formed in his models of colliding neutron stars match those
seen in our Solar System. This provides strong evidence that most of
the gold and platinum on Earth was formed in the violent collisions of
distant stars.
Dr. Rosswog says, "This is an incredible result. It's exciting to
think that the gold in wedding rings was formed far away by colliding
stars."
Professor Andrew King (Director of UKAFF at University of Leicester)
says, "This fascinating result shows that the new UKAFF supercomputer
is keeping the UK at the forefront of world astronomy."
BACKGROUND INFORMATION
The United Kingdom Astrophysical Fluids Facility (UKAFF) is a 5.9
million pound project funded jointly by the government and the
computer company SGI, with further support from the Particle Physics
and Astronomy Research Council and the Leverhulme Trust.
The facility was formally opened by Dr John Taylor, Director General
of the UK Research Councils, on October 31st, 2000.
CONTACT
Dr. Stephan Rosswog
Department of Physics and Astronomy
University of Leicester
University Road
Leicester
LE1 7RH
Phone: +44 (0)116-223-1219
E-mail: sro@star.le.ac.uk
Prof. Andrew King (same address)
Phone: +44 (0)116-252-2072
E-mail: ark@star.le.ac.uk
Images and videos can be found here.
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